Technical Field
The present invention relates to an ultrasound diagnosis apparatus, and in particular to processing of a received signal.
Related Art
An array-type ultrasound transducer (array transducer) having an array of transducer elements comprising a plurality of transducer elements is known. In addition, in order to reduce side lobes of ultrasound beam during transmission and reception of the ultrasound using the array transducer, a technique is known in which weights are assigned according to positions of the transducer elements in a transmit aperture or a receive aperture.
For example, JP Hei 7-116163 A (Patent Document 1) discloses a technique of reception weighting in which the distribution of the weights is set symmetrical. In Patent Document 1, a position of a peak of the reception weights and the position of the center of the receive aperture are matched regardless of the position of the ultrasound beam (refer to FIG. 9 of Patent Document 1).
JP 2005-253699A (Patent Document 2) and JP 2008-43531A (Patent Document 3) disclose weighting techniques in which the distribution of the weights is not symmetrical. For example, Patent Document 2 discloses that, when the ultrasound beam direction is steered in a slanted direction, a gain difference is caused in signals in the transducer elements according to the change of the path of the ultrasound, and that, in order to correct this gain difference, weights which are not symmetrical (asymmetrical weights) are used. Patent Document 3 discloses a technique to inhibit temperature increase in the probe by alternately switching between asymmetrical weights.
When the distribution of the weights is set symmetrical and the position of the peak of the reception weights and the position of the center of the receive aperture are matched regardless of the position of the ultrasound beam, if the position of the peak of the reception weights is significantly deviated from the position of the ultrasound beam, problems may be caused such as reduction of sensitivity and increase in grating lobe. Such problems cannot be solved by simply setting the distribution of the weights to be asymmetrical.
Under the above-described circumstances, the present inventors have researched and developed weights for the array transducer.